I have a question about Delta-Sigma ADC. We were evaluated for each resolution 20bit, 19bit, 18bit of by DelSig_I2C project use of AN84783, but does not seem to be normally distributed If you look at the histogram of 18bit. Effective resolution's are significantly lower for this, but I can solve what if? Evaluation environment of I is as follows. -Use development board: CY8CKIT-050 · I have been short-circuited input http://jp.cypress.com/?rID=82678

In the english manual for AN84783 here: www.cypress.com/ you find on page 10 a note concerning noise. Did you check and measure all of that discussed major noise sources and verified that each of them (and the sum) is smaller than your wanted noise level. Remember that 20 bit resolution @ Vref = 1.024V is equivalent to ca. 1µV/Lsb. Checking noise and ripple is done best using an oscilloscope, AC nd high gain and look for the level of the overshoots.

Thank you for reply. Though it is normal distribution with a resolution of 20bit, it is not a normal distribution it's a resolution of 18bit. By not become a normal distribution even when the resolution of 20bit if there is noise in the input? I think noise is the lowest input of the ADC because it short.

...and the shorting wire is not able to catch up some noise? How did you wire the cap for bypassing the Vref??

We are talking about µV, this is quite less than what you get when you near your hand to a high impendance input. You shorted the inpiut pins. Shorted to what? Ground?? Shorted, but left floating??? The application note clearly states that even the noise margin of a resistor would be too much and that you need a precision voltage source to be able to measure the performance of the ADC correctly.